Determining actual loop gain in a distributed antenna system (das)

ABSTRACT

In a wireless distribution system, a test signal(s) having a first power level is injected from a first contact point. The test signal(s) is configured to propagate from the first contact point to a second contact point over a downlink path and an uplink path, thus creating a signal loop(s). A second power level of the test signal(s) is measured at the second contact point, and an actual loop gain of the wireless distribution system is determined by subtracting the first power level from the second power level. By determining the actual loop gain of the wireless distribution system, it is possible to further determine a gain margin of the wireless distribution system. Based on the gain margin, it is possible to determine optimization possibilities for the wireless distribution system to maximize capacity and performance of the wireless distribution system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/157,970, filed May 18, 2016, which claims the benefit of priorityunder 35 U.S.C. § 119 of U.S. Provisional App. No. 62/169,267, filed onJun. 1, 2015, the contents of which are relied upon and incorporatedherein by reference in their entireties.

BACKGROUND

The disclosure relates generally to distributed antenna systems (DAS),and more particularly to techniques for measuring gain within the DAS.

Wireless customers are increasingly demanding digital data services,such as streaming video signals. At the same time, some wirelesscustomers use their wireless communication devices in areas that arepoorly serviced by conventional cellular networks, such as insidecertain buildings or areas where there is little cellular coverage. Oneresponse to the intersection of these two concerns has been the use ofDASs. A DAS is a wireless communications distribution system. A DASincludes a plurality of remote antenna units (RAUs) each configured toreceive and transmit communications signals to client devices within theantenna range of the RAUs. A DAS can be particularly useful whendeployed inside buildings or other indoor environments where thewireless communication devices may not otherwise be able to effectivelyreceive radio frequency (RF) signals from a source.

In this regard, FIG. 1 illustrates distribution of communicationsservices to remote coverage areas 100(1)-100(N) of a DAS 102, wherein‘N’ is the number of remote coverage areas. These communicationsservices can include cellular services, wireless services, such as RFidentification (RFID) tracking, Wireless Fidelity (Wi-Fi), local areanetwork (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth,Wi-Fi Global Positioning System (GPS) signal-based, and others) forlocation-based services, and combinations thereof, as examples. Theremote coverage areas 100(1)-100(N) may be remotely located. In thisregard, the remote coverage areas 100(1)-100(N) are created by andcentered on RAUs 104(1)-104(N) connected to a head-end equipment (HEE)106 (e.g., a head-end controller, a head-end unit, or a central unit).The HEE 106 may be communicatively coupled to a signal source 108, forexample, a base transceiver station (BTS) or a baseband unit (BBU). Inthis regard, the HEE 106 receives downlink communications signals 110Dfrom the signal source 108 to be distributed to the RAUs 104(1)-104(N).The RAUs 104(1)-104(N) are configured to receive the downlinkcommunications signals 110D from the HEE 106 over a communicationsmedium 112 to be distributed to the respective remote coverage areas100(1)-100(N) of the RAUs 104(1)-104(N). In a non-limiting example, thecommunications medium 112 may be a wired communications medium, awireless communications medium, or an optical fiber-based communicationsmedium. Each of the RAUs 104(1)-104(N) may include an RFtransmitter/receiver (not shown) and a respective antenna 114(1)-114(N)operably connected to the RF transmitter/receiver to wirelesslydistribute the communications services to client devices 116 within therespective remote coverage areas 100(1)-100(N). The RAUs 104(1)-104(N)are also configured to receive uplink communications signals 110U fromthe client devices 116 in the respective remote coverage areas100(1)-100(N) to be distributed to the signal source 108. The size ofeach of the remote coverage areas 100(1)-100(N) is determined by amountof RF power transmitted by the respective RAUs 104(1)-104(N), receiversensitivity, antenna gain, and RF environment, as well as by RFtransmitter/receiver sensitivity of the client devices 116. The clientdevices 116 usually have a fixed maximum RF receiver sensitivity, sothat the above-mentioned properties of the RAUs 104(1)-104(N) mainlydetermine the size of the respective remote coverage areas100(1)-100(N).

With continuing reference to FIG. 1, when the DAS 102 is configured tooperate based on frequency division duplexing (FDD), the downlinkcommunications signals 110D and the uplink communications signals 110Uare communicated between the HEE 106 and the RAUs 104(1)-104(N) overdownlink path(s) 118 and uplink path(s) 120, respectively. Sinceisolation between the downlink path(s) 118 and the uplink path(s) 120may be limited, energy from the downlink path(s) 118 may leak into theuplink path(s) 120 and subsequently loop back to the downlink path(s)118, thus causing the downlink communications signals 110D to gain extraenergy. This extra energy gain resulted from energy leaked from thedownlink path(s) 118 to the uplink path(s) 120 and looped back to thedownlink path(s) 118 is hereinafter referred to as a loop gain. The loopgain can distort the downlink communications signals 110D. As a result,under certain gain and phase shift conditions (e.g., conditionsaccording to the Barkhausen stability criterion), the downlinkcommunications signals 110D and the uplink communications signals 110Uin the DAS 102 may start oscillating. As a result, the DAS 102 maybecome unstable.

By designing and configuring the DAS 102 based on the generic loop gain,it is possible to minimize distortions to the downlink communicationssignals 110D resulting from the energy feedback, thus enabling stableoperations of the DAS 102. Generic loop gain is defined in this contextas a worst-case loop gain of the DAS 102. In this regard, the genericloop gain is defined based on the assumptions that the number of RAUs104(1)-104(N) is large, and isolations between the downlink path(s) 118and the uplink path(s) 120 (and vise versa) are minimal. However, bydesigning and configuring the DAS 102 based on the worst-case loop gain,it may lead to under-configuration and underutilization of the DAS 102.

No admission is made that any reference cited herein constitutes priorart. Applicant expressly reserves the right to challenge the accuracyand pertinency of any cited documents.

SUMMARY

Embodiments of the disclosure relate to determining actual loop gain ina distributed antenna system (DAS). The DAS receives at least onecommunications service from at least one signal source (e.g., a basestation or baseband unit (BBU), and includes a head end unit (HEU) and aplurality of remote antenna units (RAUs). Actual loop gain is a powerdifferential of a test signal(s) measured at two different contactpoints in a HEU in a DAS. In this regard, a downlink path in the HEU isdisconnected to create a first contact point and a second contact point.The test signal(s) having a first power level is injected from the firstcontact point. The test signal(s) propagates over the downlink path(s)in the DAS from the first contact point to an RAU(s), and returns fromthe RAU(s) to the second contact point in the HEU over an uplink path,thus creating a signal loop(s). A second power level of the testsignal(s) is measured at the second contact point to determine theactual loop gain of the DAS. The actual loop gain of the DAS isdetermined by subtracting the first power level from the second powerlevel. By determining the actual loop gain of the DAS, it is possible tofurther determine a gain margin of the DAS. Based on the gain margin, itis possible to determine optimization possibilities (e.g., determine amargin of gain by comparing the actual loop gain against a predeterminedthreshold) for the DAS to maximize capacity and performance of the DAS.

One embodiment of the disclosure relates to a DAS configured to enableactual loop gain measurement. The DAS comprises a plurality of RAUs. TheDAS also comprises an HEU. The HEU is configured to distribute adownlink signal to at least one RAU among the plurality of RAUs. The HEUis also configured to receive an uplink signal from the at least oneRAU. The DAS also comprises a switch circuit disposed in a downlink pathin the HEU and configured to disconnect the downlink path into a firstcontact point and a second contact point. The DAS also comprises asignal generator communicatively coupled to the first contact point. Thesignal generator is configured to provide at least one test signalhaving a first power level to the first contact point for distributionto the at least one RAU on the downlink path. The DAS also comprises areceiver communicatively coupled to the second contact point. Thereceiver is configured to receive at least one loopback test signalhaving a second power level from the second contact point. The receiveris also configured to determine a difference between the first powerlevel of the at least one test signal at the first contact point and thesecond power level of the at least one loopback test signal at thesecond contact point. The receiver is also configured to determine anactual loop gain of the DAS based on the determined difference betweenthe first power level and the second power level.

Another embodiment of the disclosure relates to a method for measuringactual loop gain in a DAS. The method comprises disconnecting a downlinkpath in an HEU into a first contact point and a second contact point.The method also comprises providing at least one test signal having afirst power level from the first contact point to at least one RAU inthe DAS on the downlink path. The method also comprises receiving atleast one loopback test signal having a second power level from thesecond contact point. The method also comprises determining a differencebetween the first power level of the at least one test signal at thefirst contact point and the second power level of the at least oneloopback test signal at the second contact point. The method alsocomprises determining an actual loop gain of the DAS based on thedetermined difference between the first power level and the second powerlevel.

Additional features and advantages will be set forth in the detaileddescription which follows and, in part, will be readily apparent tothose skilled in the art from the description or recognized bypracticing the embodiments as described in the written description andclaims hereof, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary and are intendedto provide an overview or framework to understand the nature andcharacter of the claims.

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiment(s), and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates distribution of communications services to remotecoverage areas of a distributed antenna system (DAS);

FIG. 2 is a schematic diagram of an exemplary DAS including one or moresignal loops indicating potential loop gains generated by variouscomponents provided in a downlink path and an uplink path between a headend unit (HEU) and a plurality of remote antenna units (RAUs);

FIG. 3 is a schematic diagram of an exemplary DAS configured to enablemeasurement of an actual loop gain (G_(LA)) of the DAS based ondetermining the difference in power level of at least one test signalinjected into the DAS at a first contact point in the DAS and receivedat a second contact point in the DAS;

FIG. 4 is a flowchart of an exemplary actual loop gain determinationprocess for determining the actual loop gain (G_(LA)) of the DAS in FIG.3 based on determining the difference in power level of the at least onetest signal injected into the DAS at the first contact point in the DASand received at the second contact point in the DAS

FIG. 5 is a schematic diagram of an exemplary DAS configured to enablemeasurement of the actual loop gain (G_(LA)) of the DAS in FIG. 3 basedon the at least one test signal that propagates along a plurality ofsignal loops;

FIG. 6 is a graph providing an exemplary illustration of a plurality ofpower level markers at a plurality of frequencies that is part of anexemplary frequency spectrum of the DAS of FIG. 5;

FIG. 7 is an exemplary interactive graphical user interface (GUI) that acomputing device may employ to interact with an operator/engineer formeasuring the actual loop gain (G_(LA)) in the DASs of FIGS. 3 and 5;

FIG. 8 is a schematic diagram of an exemplary DAS that can be configuredto function as the DASs of FIGS. 3 and 5;

FIG. 9 is a schematic diagram of an exemplary optical fiber-based DASconfigured to enable measurement of an actual loop gain (G_(LA)) basedon determining the difference in power level of at least one test signalinjected into the DAS at the first contact point in the DAS and receivedat the second contact point in the DAS; and

FIG. 10 is a partial schematic cut-away diagram of an exemplary buildinginfrastructure in which DASs configured to enable measurement of theactual loop gain (G_(LA)), including the DASs of FIGS. 3 and 5, can beprovided.

DETAILED DESCRIPTION

Embodiments of the disclosure relate to determining actual loop gain ina distributed antenna system (DAS). The DAS receives at least onecommunications service from at least one signal source (e.g., a basestation or baseband unit (BBU), and includes a head end unit (HEU) and aplurality of remote antenna units (RAUs). Actual loop gain is a powerdifferential of a test signal(s) measured at two different contactpoints in a HEU in a DAS. In this regard, a downlink path in the HEU isdisconnected to create a first contact point and a second contact point.The test signal(s) having a first power level is injected from the firstcontact point. The test signal(s) propagates over the downlink path(s)in the DAS from the first contact point to an RAU(s), and returns fromthe RAU(s) to the second contact point in the HEU over an uplink path,thus creating a signal loop(s). A second power level of the testsignal(s) is measured at the second contact point to determine theactual loop gain of the DAS. The actual loop gain of the DAS isdetermined by subtracting the first power level from the second powerlevel. By determining the actual loop gain of the DAS, it is possible tofurther determine a gain margin of the DAS. Based on the gain margin, itis possible to determine optimization possibilities (e.g., determine amargin of gain by comparing the actual loop gain against a predeterminedthreshold) for the DAS to maximize capacity and performance of the DAS.

Before discussing examples of determining actual loop gain in a DASstarting at FIG. 3, an overview of an exemplary DAS having loop gainsassociated with downlink and uplink paths is first discussed withreference to FIG. 2. The discussion of specific exemplary aspects ofdetermining actual loop gain of a DAS starts with reference to FIG. 3.

In this regard, FIG. 2 is a schematic diagram of an exemplary DAS 200including one or more signal loops 202(1)-202(N) indicating potentialloop gains generated by various components provided in a downlink path204 and an uplink path 206 between a head end unit (HEU) 208 and aplurality of RAUs 210(1)-210(N). With reference to FIG. 2, the HEU 208includes one or more radio interface modules (RIMs) 212(1)-212(M) thatare communicatively coupled to one or more radio sources 214(1)-214(M),respectively. In a non-limiting example, each of the radio sources214(1)-214(M) is configured to provide a respective wirelesscommunication service, such as long-term evolution (LTE) and widebandcode division multiple access (WCDMA). The RIMs 212(1)-212(M) areconfigured to receive one or more downlink communications signals216(1)-216(M) from the radio sources 214(1)-214(M), respectively. In anon-limiting example, the downlink communications signals 216(1)-216(M)correspond to a plurality of frequency bands (not shown), including LTEfrequency bands, personal communications service (PCS) frequency bands,and/or advanced wireless service (AWS) frequency bands. The RIMs212(1)-212(M) are also configured to provide one or more uplinkcommunications signals 218(1)-218(M) to the radio sources 214(1)-214(M),respectively. The RIMs 212(1)-212(M) include one or more HEU duplexers220(1)-220(M), one or more RIM downlink circuits 222(1)-222(M), and oneor more RIM uplink circuits 224(1)-224(M), respectively. In anon-limiting example, the RIM downlink circuits 222(1)-222(M) areconfigured to perform frequency filtering and conversion (e.g.,frequency downshift or upshift) on the downlink communications signals216(1)-216(M), respectively, before distributing the downlinkcommunications signals 216(1)-216(M) on the downlink path 204. Likewise,the RIM uplink circuits 224(1)-224(M) are configured to performfrequency filtering and conversion (e.g., frequency downshift orupshift) on the uplink communications signals 218(1)-218(M) received onthe uplink path 206 before providing the uplink communications signals218(1)-218(M) to the radio sources 214(1)-214(M), respectively. In thisregard, the HEU duplexers 220(1)-220(M) couple the RIM downlink circuits222(1)-222(M) to the radio sources 214(1)-214(M) to receive the downlinkcommunications signals 216(1)-216(M), respectively. The HEU duplexers220(1)-220(M) also couple the RIM uplink circuits 224(1)-224(M) to theradio sources 214(1)-214(M) to provide the uplink communications signals218(1)-218(M) to the radio sources 214(1)-214(M), respectively.

With continuing reference to FIG. 2, the HEU 208 includes a downlinkcombiner 226 and a downlink splitter 228. The downlink combiner 226 andthe downlink splitter 228 are disposed in the downlink path 204. Thedownlink combiner 226 is configured to combine the downlinkcommunications signals 216(1)-216(M) to generate a combined downlinkcommunications signal 230. The downlink splitter 228 is configured toreceive the combined downlink communications signal 230 from thedownlink combiner 226 and generate a plurality of downlink electricalsignals 232(1)-232(N) for distribution to the RAUs 210(1)-210(N),respectively. In a non-limiting example, each of the RAUs 210(1)-210(N)is configured to communicate at a predetermined set of frequencychannels/bands. As such, the downlink splitter 228 splits the downlinkcommunications signals 216(1)-216(M) into the downlink electricalsignals 232(1)-232(N) based on the predetermined set of frequencychannels/bands associated with each of the RAUs 210(1)-210(N).

The RAUs 210(1)-210(N) include a plurality of RAU downlink circuits234(1)-234(N), a plurality of RAU uplink circuits 236(1)-236(N), and aplurality of RAU duplexers 238(1)-238(N), respectively. The RAUduplexers 238(1)-238(N) are communicatively coupled to a plurality ofantennas 240(1)-240(N), respectively. In a non-limiting example, theantennas 240(1)-240(N) are multiple-input, multiple-output (MIMO)antennas. The RAU downlink circuits 234(1)-234(N) receive and providethe downlink electrical signals 232(1)-232(N) to the RAU duplexers238(1)-238(N), respectively. The RAU duplexers 238(1)-238(N) in turnprovide the downlink electrical signals 232(1)-232(N) to the antennas240(1)-240(N), respectively, for distribution to client devices (notshown) in the DAS 200.

With continuing reference to FIG. 2, the RAU duplexers 238(1)-238(N) areconfigured to receive a plurality of uplink electrical signals242(1)-242(N) from the antennas 240(1)-240(N) and provide the uplinkelectrical signals 242(1)-242(N) to the RAU uplink circuits236(1)-236(N), respectively. In a non-limiting example, the RAUduplexers 238(1)-238(N) do not have sufficient isolations between thedownlink electrical signals 232(1)-232(N) and the uplink electricalsignals 242(1)-242(N), respectively. As a result, the downlinkelectrical signals 232(1)-232(N) may leak from the downlink path 204into the uplink path 206, thus contributing to the loop gains on thesignal loops 202(1)-201(N), respectively.

With continuing reference to FIG. 2, the HEU 208 includes an uplinkcombiner 244 and an uplink splitter 246. The uplink combiner 244receives the uplink electrical signals 242(1)-242(N) from the RAUs210(1)-210(N), respectively. The uplink combiner 244 combines the uplinkelectrical signals 242(1)-242(N) to generate a combined uplinkcommunications signal 248. The uplink splitter 246 splits the combineduplink communications signal 248 to generate the uplink communicationssignals 218(1)-218(M). The RIM uplink circuits 224(1)-224(M) receive theuplink communications signals 218(1)-218(M) and provide the uplinkcommunications signals 218(1)-218(M) to the HEU duplexers 220(1)-220(M),respectively. The HEU duplexers 220(1)-220(M) provide the uplinkcommunications signals 218(1)-218(M) to the radio sources 214(1)-214(M),respectively. In a non-limiting example, the HEU duplexers 220(1)-220(M)do not have sufficient isolations between the downlink communicationssignals 216(1)-216(M) and the uplink communications signals218(1)-218(M), respectively. As a result, the uplink communicationssignals 218(1)-218(M) may leak from the uplink path 206 into thedownlink path 204, thus contributing to the loop gains on the signalloops 202(1)-202(N), respectively.

With continuing reference to FIG. 2, each of the signal loops202(1)-202(N) produces a respective loop gain. As such, the actual loopgain (G_(LA)) of the DAS 200 is a sum of the respective loop gainsproduced by the signal loops 202(1)-202(N). The loop gains from thesignal loops 202(1)-202(N) can distort the downlink communicationssignals 216(1)-216(M). As a result, under certain gain and phase shiftconditions (e.g., conditions according to the Barkhausen stabilitycriterion), the downlink communications signals 216(1)-216(M) and theuplink communications signals 218(1)-218(M) in the DAS 200 may startoscillating. As a result, the DAS 200 may become unstable.

As can be seen in FIG. 2, the signal loops 202(1)-202(N) converge at aphysical link 250, which is a coaxial cable for example, connecting thedownlink combiner 226 and the downlink splitter 228. As such, it ispossible to measure the actual loop gain of the DAS 200 at the physicallink 250 by breaking up the physical link 250 to create two contactpoints and measure a power differential of a test signal injected fromone contact point and propagated to another contact point. In thisregard, FIG. 3 is a schematic diagram of an exemplary DAS 300 configuredto enable measurement of an actual loop gain (G_(LA)) based on at leastone test signal 302.

With reference to FIG. 3, the DAS 300 includes an HEU 304 and aplurality of RAUs 306(1)-306(N). The RAU 306(1) is discussed hereinafteras a non-limiting example. The HEU 304 includes a downlink combiner 308,a downlink splitter 310, an uplink combiner 312, and an uplink splitter314. The HEU 304 includes at least one RIM 316 that includes an RIMdownlink circuit 318 and an RIM uplink circuit 320. In a non-limitingexample, the downlink combiner 308 is functionally equivalent to thedownlink combiner 226 of FIG. 2. The downlink splitter 310 isfunctionally equivalent to the downlink splitter 228 of FIG. 2. Theuplink combiner 312 is functionally equivalent to the uplink combiner244 of FIG. 2. The uplink splitter 314 is functionally equivalent to theuplink splitter 246 of FIG. 2. The RIM 316 is functionally equivalent toany of the RIMs 212(1)-212(M) of FIG. 2. The RIM downlink circuit 318 isfunctionally equivalent to any of the RIM downlink circuits222(1)-222(M) of FIG. 2. The RIM uplink circuit 320 is functionallyequivalent to any of the RIM uplink circuits 224(1)-224(M) of FIG. 2.The RAU 306(1) includes an RAU duplexer 322, an RAU downlink circuit324, an RAU uplink circuit 326, and an antenna 328. In a non-limitingexample, the antenna 328 is a MIMO antenna. The RAU duplexer 322 isfunctionally equivalent to any of the RAU duplexers 238(1)-238(N) ofFIG. 2. The RAU downlink circuit 324 is functionally equivalent to anyof the RAU downlink circuits 234(1)-234(N) of FIG. 2. The RAU uplinkcircuit 326 is functionally equivalent to any of the RAU uplink circuits236(1)-236(N) of FIG. 2. The antenna 328 is functionally equivalent toany of the antennas 240(1)-240(N) of FIG. 2.

The DAS 300 includes a downlink path 330 and an uplink path 332. Thedownlink combiner 308 and the downlink splitter 310 are connected by alink 334, which is a coaxial cable, for example. A switch circuit 336,which is a broadband switch circuit having broadband isolation in anon-limiting example, is disposed in the downlink path 330. The switchcircuit 336 is configured to disconnect (i.e., break) the downlink path330 into a first contact point 338 and a second contact point 340. Assuch, the test signal 302 is injected at the first contact point 338 andpropagates to the second contact point 340 as a loopback test signal302′. Accordingly, a power differential of the test signal 302 at thefirst contact point 338 and the loopback test signal 302′ at the secondcontact point 340 can be measured to determine the actual loop gain(G_(LA)). In a non-limiting example, the switch circuit 336 is providedon a portion of the downlink path 330 that is between the downlinkcombiner 308 and the downlink splitter 310. This is because the portionof the downlink path 330 between the downlink combiner 308 and thedownlink splitter 310 is the downlink pathway of all downlinkcommunications signals (e.g., the downlink communications signals216(1)-216(M) of FIG. 2) communicating from the HEU 304 to the RAUs306(1)-306(N). Therefore, by providing the switch circuit 336 at theportion of the downlink path 330 between the downlink combiner 308 andthe downlink splitter 310, it is possible to measure the actual loopgain (G_(LA)) with the test signal 302 in a condition closer to actualoperating conditions of the DAS 300. In this regard, the switch circuit336 decouples the downlink combiner 308 and the downlink splitter 310from the link 334 to allow only the test signal 302 to propagate via thedownlink path 330 and loop back via the uplink path 332 in the DAS 300.In this regard, the test signal 302 is a downlink signal and theloopback signal 302′ is an uplink signal.

With continuing reference to FIG. 3, a signal generator 342 iscommunicatively coupled to the first contact point 338 and configured toprovide the test signal 302 for distribution to the RAU 306(1) on thedownlink path 330. The signal generator 342 is configured to generatethe test signal 302 of known characteristics (e.g., center frequency,bandwidth, etc.). In a non-limiting example, the signal generator 342 iscoupled to the first contact point 338 by a first communications link344, which may be a coaxial cable for example. The test signal 302propagates from the first contact point 338 to the RAU duplexer 322 inthe RAU 306(1). In a non-limiting example, the RAU duplexer 322 does nothave sufficient isolation between the downlink path 330 and the uplinkpath 332. As a result, a portion or a whole of the test signal 302 mayleak into the uplink path 332, thus generating the loopback test signal302′ in the uplink path 332.

A receiver 346 is communicatively coupled to the second contact point340 to receive the loopback test signal 302′ from the RAU 306(1) overthe uplink path 332. In a non-limiting example, the receiver 346 iscoupled to the second contact point 340 by a second communications link348, which may also be a coaxial cable. In this regard, the test signal302 that propagates from the first contact point 338 to the RAU duplexer322 and the loopback test signal 302′ that propagates from the RAUduplexer 322 to the second contact point 340 create a signal loop 350(also known as a signal path). As shown in FIG. 3, the loopback testsignal 302′ propagates from the RAU duplexer 322 to the HEU 304 via theRAU uplink circuit 326. In a non-limiting example, the RAU uplinkcircuit 326 includes a power amplifier (not shown) that increasesrespective power level of the loopback test signal 302′. As a result,the loopback test signal 302′ may have a higher power level than thetest signal 302. To allow the test signal 302 to propagate from theuplink path 332 back to the downlink path 330 and reach the secondcontact point 340, the RIM uplink circuit 320 is coupled to the RIMdownlink circuit 318 through an HEU duplexer 352. In a non-limitingexample, the HEU duplexer 352 is configured to couple the RIM uplinkcircuit 320 to the RIM downlink circuit 318 via a shunt resistor 354. Asa result, the DAS 300 is decoupled from radio sources (e.g., the radiosources 214(1)-214(M) of FIG. 2), thus making the test signal 302, andthus the loopback test signal 302′, clean test signals for determiningthe actual loop gain (G_(LA)).

In this regard, the signal loop 350 starts from the first contact point338 and ends at the second contact point 340. The signal loop 350includes the downlink splitter 310, the RAU downlink circuit 324, andthe RAU duplexer 322 in the downlink path 330. In the uplink path 332,the signal loop 350 includes the RAU uplink circuit 326, the uplinkcombiner 312, the uplink splitter 314, the RIM uplink circuit 320, andthe HEU duplexer 352. The signal loop 350 further includes the RIMdownlink circuit 318 and the downlink combiner 308.

The test signal 302 has a first power level (P₁) when the signalgenerator 342 injects the test signal 302 into the DAS 300. As the testsignal 302 propagates from the first contact point 338 towards thesecond contact point 340 along the signal loop 350, components involvedin the signal loop 350 (e.g., the RAU duplexer 322, the power amplifierin the RAU uplink circuit 326, etc.) may cause the loopback test signal302′ to gain additional power as a result of insufficient isolation inthe components. As such, the loopback test signal 302′ will have asecond power level (P₂) at the second contact point 340. The receiver346, which may be a signal analyzer for example, can thus determine theactual loop gain (G_(LA)) of the DAS 300 based on the equation (Eq. 1)below.

G _(LA) =P ₂ −P ₁   (Eq. 1)

The actual loop gain (G_(LA)) of the DAS 300 is the difference betweenthe second power level (P₂) when the loopback test signal 302′ isreceived at the second contact point 340 and the first power level (P₁)when the test signal 302 injected to the first contact point 338. Whenthe actual loop gain (G_(LA)) is greater than zero (0), it is anindication that the test signal 302 has gained power along the signalloop 350, and one or more of the components involved in the signal loop350 may be insufficiently isolated.

In a non-limiting example, the receiver 346 determines the first powerlevel (P₁) of the test signal 302 by communicating to the signalgenerator 342. In another non-limiting example, the receiver 346 and thesignal generator 342 are integrated and configured to share informationvia a shared storage media (not shown). In another non-limiting example,the receiver 346 and the signal generator 342 are embedded parts of theDAS 300. The receiver 346 and the signal generator 342 may be used alsofor other tasks such as spectrum monitoring and system gain adjustment.System gain adjustment may be performed, for example, during systemmaintenance, change-out of components and at other suitable intervals.

In a non-limiting example, the receiver 346 includes one or moreprocessors 356 and storage media 358. The processors 356 are configuredto determine the actual loop gain (G_(LA)) of the DAS 300 according tothe equation (Eq. 1). The processors 356 are further configured torecord the actual loop gain (G_(LA)) in the storage media 358. Acomputing device 360 (e.g., a laptop computer, a desktop computer, atest equipment, etc.) may be communicatively coupled to the receiver 346to retrieve the actual loop gain (G_(LA)) from the storage media 358 andpresent the actual loop gain (G_(LA)) via graphical interfaces such asliquid crystal display (LCD). In a non-limiting example, anoperator/engineer receives an indication on the gain margin (G_(M))through, for example, the computing device 360. If the gain margin(G_(M)) is positive, the DAS 300 may be tuned or modified (for example,more remote antenna units may be added) while monitoring the impact onthe gain margin (G_(M)). If the gain margin (G_(M)) is zero (ornegative) then corrective actions may be taken by the operator/engineer.

The signal generator 342 and/or the receiver 346 can be configured todetermine the actual loop gain (G_(LA)) in the DAS 300 based on aprocess. In this regard, FIG. 4 is a flowchart of an exemplary actualloop gain determination process 400 for determining the actual loop gain(G_(LA)) of the DAS 300 of FIG. 3 based on the test signal 302.

With reference to FIG. 4, the downlink path 330 in the HEU 304 isdisconnected into the first contact point 338 and the second contactpoint 340 (block 402). Next, the signal generator 342 provides the testsignal 302, which has the first power level (P₁), from the first contactpoint 338 to the RAU 306(1) on the downlink path 330 (block 404). Thereceiver 346 receives the loopback test signal 302′, which has thesecond power level (P₂), from the second contact point 340 (block 406).The receiver 346 then determines the difference between the first powerlevel (P₁) of the test signal 302 at the first contact point 338 and thesecond power level (P₂) of the loopback signal 302′ at the secondcontact point 340 (block 408). The receiver then determines the actualloop gain (G_(LA)) of the DAS 300 based on the determined differencebetween the first power level (P₁) and the second power level (P₂)(block 410).

With reference back to FIG. 3, after determining the actual loop gain(_(GLA)) of the DAS 300, the receiver 346 is able to determine a gainmargin (G_(M)) for the DAS 300 based on the equation (Eq. 2) below.

G _(M) =G _(LC) −G _(LA)   (Eq. 2)

According to equation (Eq. 2), the gain margin (G_(M)) refers to themargin between a critical loop gain (G_(LC)) and the actual loop gain(G_(LA)). The critical loop gain (G_(LC)) is a loop gain measure that,when exceeded, may cause noticeable distortion and/or instability (e.g.,oscillation) in the DAS 300. In a non-limiting example, the criticalloop gain (G_(LC)) is generally set to negative fifteen decibels (−15dB). It shall be noted that the critical loop gain (G_(LC)) may be setdifferently from one DAS to another. For example, in one DAS, a negativetwenty decibels (−20 dB) critical loop gain (G_(LC)) may be sufficientto prevent distortion and/or instability, while another DAS may requirea negative eight decibels (−8 dB) critical loop gain (G_(LC)) to preventdistortion and/or instability. In this regard, if the gain margin(G_(M)) is greater than zero (0) (G_(M)>0), it is an indication that theDAS 300 is not configured to maximum capability and/or capacity. Incontrast, if the gain margin (G_(M)) is less than or equal to 0(G_(M)≤0), it is an indication that the DAS 300 is configured overmaximum capability and/or capacity, and is thus susceptible todistortions and/or instabilities. The actual loop gain (G_(LA)) and thegain margin (G_(M)) are useful indicators that can be used to fine tunethe DAS 300 for optimal capacity and performance. As such, the loop gain(G_(LA)) and the gain margin (G_(M)) are typically determined after thecommissioning process of the DAS 300 and prior to connecting the DAS 300to radio sources (not shown) to begin commercial services.

With continuing reference to FIG. 3, in a non-limiting example, the DAS300 is an optical fiber-based DAS. In this regard, the HEU 304 includesan HEU electrical-to-optical (E/O) converter 362 on the downlink path330 and an HEU optical-to-electrical (O/E) converter 364 on the uplinkpath 332. Likewise, the RAU 306(1) includes an RAU O/E converter 366 andan RAU E/O converter 368. The HEU E/O converter 362 is configured toconvert the test signal 302 into a downlink optical test signal 370. TheRAU O/E converter 366 is configured to receive and convert the downlinkoptical test signal 370 into the test signal 302. The RAU E/O converter368 is configured to convert the test signal 302 into an uplink opticaltest signal 372 and provide the uplink optical test signal 372 to theHEU 304. The HEU O/E converter 364 is configured to receive and convertthe uplink optical test signal 372 into the test signal 302.

Aspects of measuring the actual loop gain (G_(LA)) and determining thegain margin (G_(M)) as described in reference to FIG. 3 are applicableto a DAS having a plurality RAUs. In this regard, FIG. 5 is a schematicdiagram of an exemplary DAS 500 configured to enable measurement of theactual loop gain (G_(LA)) of the DAS 300 in FIG. 3 based on the testsignal 302 that propagates along a plurality of signal loops502(1)-502(N). Common elements between FIGS. 3 and 5 are shown thereinwith common element numbers and will not be re-described herein.

With reference to FIG. 5, the DAS 500 includes an HEU 504 and aplurality of RAUs 506(1)-506(N). The RAUs 506(1)-506(N) are functionallyequivalent to the RAU 306(1)-306(N) of FIG. 3. The RAUs 506(1)-506(N)include a plurality of RAU duplexers 508(1)-508(N), a plurality of RAUdownlink circuits 510(1)-510(N), and a plurality of RAU uplink circuits512(1)-512(N), respectively. Each of the RAU duplexers 508(1)-508(N) isfunctionally equivalent to the RAU duplexer 322 of FIG. 3. Each of theRAU downlink circuits 510(1)-510(N) is functionally equivalent to theRAU downlink circuit 324 of FIG. 3. Each of the RAU uplink circuits512(1)-512(N) is functionally equivalent to the RAU uplink circuit 326of FIG. 3.

The HEU 504 includes one or more RIMs 514(1)-514(M). The RIMs514(1)-514(M) include one or more RIM downlink circuits 516(1)-516(M)and one or more RIM uplink circuits 518(1)-518(M), respectively. The RIMdownlink circuits 516(1)-516(M) are coupled to the RIM uplink circuits518(1)-518(M) via one or more HEU duplexers 520(1)-520(M), respectively.In a non-limiting example, the HEU duplexers 520(1)-520(M) include oneor more shunt resistors 522(1)-522(M), respectively. The shunt resistors522(1)-522(M) are configured to provide proper terminations to the RIMdownlink circuits 516(1)-516(M) and the RIM uplink circuits518(1)-518(M), respectively. As such, the DAS 500 is decoupled from oneor more radio sources 524(1)-524(M), thus making the test signal 302 andthe loopback test signal 302′ clean test signals for determining theactual loop gain (G_(LA)).

With continuing reference to FIG. 5, the signal generator 342 injectsthe test signal 302 into the DAS 500 from the first contact point 338.The test signal 302, which has the first power level (P₁), propagatesfrom the first contact point 338 to the second contact point 340 alongthe signal loops 502(1)-502(N). The receiver 346 is configured toreceive the loopback test signal 302′ at the second contact point 340and measure the second power level (P₂) of the loopback test signal302′. The receiver 346 can thus determine the actual loop gain (G_(LA))of the DAS 500 according to Eq. 1 above. Since the test signal 302propagates along the signal loops 502(1)-502(N), the actual loop gain(G_(LA)) of the DAS 500 is a sum of respective loop gains produced bythe signal loops 502(1)-502(N). Accordingly, the receiver 346 candetermine the gain margin (G_(M)) of the DAS 500 based on Eq. 2 above.According to previous discussions in FIG. 3, if the gain margin (G_(M))is greater than 0 (G_(M)>0), it is an indication that the DAS 500 is notconfigured to maximum capability and/or capacity. In contrast, if thegain margin (G_(M)) is less than or equal to 0 (G_(M)≤0), it is anindication that the DAS 500 is configured over maximum capability and/orcapacity, and is thus susceptible to distortions and/or instabilities.

With continuing reference to FIG. 5, the DAS 500 may be configured tosupport a plurality of wireless communications services in a variety offrequency bands. For example, the DAS 500 is configured to provide LTEservices and/or WCDMA services. Accordingly, the DAS 500 is configuredto operate in LTE frequency bands, personal communications service (PCS)frequency band, and/or advanced wireless service (AWS) frequency bands.In a non-limiting example, the DAS 500 is configured to operate in afrequency-division duplexing (FDD) mode that requires at least onedownlink frequency band and at least one uplink frequency band tofunction. For example, the PCS frequency band includes an uplinkfrequency band, which ranges from one thousand eight hundred fiftymegahertz (1850 MHz) to one thousand nine hundred fifteen megahertz(1915 MHz), and a downlink frequency band, which ranges from onethousand nine hundred thirty megahertz (1930 MHz) to one thousand ninehundred ninety-five megahertz (1995 MHz). In this regard, it isnecessary to determine the actual loop gain (G_(LA)) based on thefrequency band(s) in which the DAS 500 is designed to operate.

As such, the signal generator 342 may be configured to generate the testsignal 302 that corresponds to at least one downlink frequency band 526D(e.g., the 1930-1995 MHz PCS downlink band) and at least one uplinkfrequency band 526U (e.g., the 1850-1915 MHz PCS uplink band). Thedownlink frequency band 526D corresponds to a downlink center frequency(f_(DC)) and a downlink frequency bandwidth (W_(D)). The uplinkfrequency band 526U corresponds to an uplink center frequency (f_(UC))and an uplink frequency bandwidth (W_(U)). A cross band frequency(f_(CB)) is the middle point frequency between the downlink centerfrequency (f_(DC)) and the uplink center frequency (f_(UC))(f_(CB)=(f_(DC)+f_(UC))/2).

Continuing with the PCS frequency band example, the downlink centerfrequency (f_(DC)) and the uplink center frequency (f_(UC)) are onethousand nine hundred sixty-two point five megahertz (1962.5 MHz) andone thousand eight hundred eighty-two point five megahertz (1882.5 MHz),respectively. Accordingly, the cross band frequency (fCB) is onethousand nine hundred twenty-two point five megahertz (1922.5 MHz). Inthis regard, to determine the actual loop gain (G_(LA)) for the PCSfrequency band, the signal generator 342 needs to generate the testsignal 302 that corresponds to the downlink frequency band (1930-1995MHz) and the uplink frequency band (1850-1915 MHz) of the PCS frequencyband.

As previously mentioned, the DAS 500 may be configured to operate inadditional frequency bands, such as the LTE frequency band and the AWSfrequency band, for example. In this regard, it may be possible that theRAU 506(1) is configured to operate on the PCS frequency band, the RAU506(2) is configured to operate on the LTE frequency band, and the RAU506(N) is configured to operate on the AWS frequency band. In anon-limiting example, these additional frequency bands may haverespective cross band frequency (f_(CB)) located throughout thefrequency spectrum of the DAS 500. To determine the actual loop gain(G_(LA)) in the context of all the downlink and uplink frequency bandswhich the RAUs 506(1)-506(N) are configured to support, the test signal302 propagating along the signal loops 502(1)-502(N) needs to cover theentire frequency spectrum of the DAS 500. In this regard, in anon-limiting example, if the DAS 500 is configured to support afrequency spectrum ranging from four hundred fifty megahertz (450 MHz)to two thousand seven hundred megahertz (2700 MHz), the signal generator342 needs to generate the test signal 302 by sweeping the frequencyspectrum of the DAS 500. In this regard, the test signal 302 is a narrowband signal corresponding to a respective cross band frequency (f_(CB)).

With continuing reference to FIG. 5, the receiver 346 receives the testsignal 302 having the second power level (P₂). As such, when the signalgenerator 342 sweeps the frequency spectrum of the DAS 500, the receiver346 is able to determine the second power level (P₂) of the test signal302 at both cross band frequencies (f_(CB)) and non-cross bandfrequencies. For purpose of distinction, the second power level (P₂)corresponding to the cross band frequencies (f_(CB)) is hereinafterreferred to as a cross band power level.

In a non-limiting example, the cross band power level can be graphed andvisualized on the computing device 360. In this regard, FIG. 6 is agraph 600 providing an exemplary illustration of a plurality of powerlevel markers 602(1)-602(5) (also known as markers) at a plurality offrequencies 604(1)-604(5) that is part of the frequency spectrum of theDAS 500 of FIG. 5. Common elements of FIG. 5 are referenced inconnection with FIG. 6 and will not be re-described herein.

With reference to FIG. 6, the graph 600 illustrates power level of thetest signal 302 (Y-axis) as a function of frequency (f) of the testsignal 302 (X-axis). In FIG. 6, the range for the power level is betweennegative one hundred decibels (−100 dB) and zero decibels (0 dB), whilethe range of the frequency (f) is between four hundred fifty megahertz(450 MHz) and two thousand seven hundred megahertz (2700 MHz or 2.7GHz). As illustrated in FIG. 6, the power level markers 602(1)-602(5)indicate that the test signal 302 peaks at the frequencies604(1)-604(5). In a non-limiting example, the frequencies 604(1)-604(5)correspond to approximately six hundred six megahertz (606 MHz), sevenhundred twenty-one megahertz (721 MHz), eight hundred sixty-twomegahertz (862 MHz), one thousand nine hundred twenty megahertz (1920MHz), and two thousand one hundred twenty-one megahertz (2121 MHz),respectively. Among the frequencies 604(1)-604(5), the frequencies604(1)-604(4) are cross band frequencies (f_(CB)), but the frequency604(5) is not a cross band frequency (f_(CB)).

Accordingly, the power level markers 602(1)-602(4) corresponding to thecross band frequencies (f_(CB)) 604(1)-604(4) are cross band power levelmarkers. Among them, the cross band power level marker 602(2)corresponds to the 721 MHz LTE cross band frequency (f_(CB)). The crossband power level marker 602(1) corresponds to the 606 MHz cross bandfrequency (f_(CB)), which is the same as a seven hundred twenty-onemegahertz (721 MHz) LTE cross band frequency (f_(CB)), but multiplexedand synthesized to transmit with the 721 MHz LTE cross band frequency(f_(CB)) over an optical fiber. The cross band power level marker 602(3)corresponds to the 862 MHz cross band frequency (f_(CB)). The cross bandpower level marker 602(4) corresponds to a one thousand nine hundredtwenty-two point five megahertz (1922.5 MHz) PCS cross band frequency(f_(CB)). The power level marker 602(5), however, does not correspond toa cross band frequency (f_(CB)) and may result from noise in the DAS500.

As illustrated in the graph 600, the cross band power level at the crossband frequency (f_(CB)) 604(1) is negative sixty-one decibels (−61 dB).Accordingly, a margin of gain (MG) at the cross band frequency (f_(CB))604(1) can be determined based on the equation (Eq. 3) below.

M _(G)=(Cross Band Power Level)−(Predetermined Threshold)   (Eq. 3)

In a non-limiting example, the predetermined threshold is the same asthe critical loop gain (G_(LC)) as previously discussed. As such, if thepredetermined threshold is −20 dB, then the margin of gain (M_(G)) atthe cross band frequency (f_(CB)) 604(1) is negative forty-one decibels(−41 dB) according to equation (Eq. 3).

In another non-limiting example, the cross band power level at the crossband frequency (f_(CB)) 604(2) is negative forty-two decibels (−42 dB).As such, if the predetermined threshold is −20 dB, then the margin ofgain (M_(G)) at the cross band frequency (f_(CB)) 604(2) is negativetwenty-two decibels (−22 dB) according to equation (Eq. 3).

In another non-limiting example, the cross band power level at the crossband frequency (f_(CB)) 604(3) is negative fifty-four decibels (−54 dB).As such, if the predetermined threshold is −20 dB, then the margin ofgain (M_(G)) at the cross band frequency (f_(CB)) 604(3) is negativethirty-four decibels (−34 dB) according to equation (Eq. 3).

In another non-limiting example, the cross band power level at the crossband frequency (f_(CB)) 604(4) is −34 dB. As such, if the predeterminedthreshold is −20 dB, the margin of gain (M_(G)) at the cross bandfrequency (f_(CB)) 604(4) is negative fourteen decibels (−14 dB)according to equation (Eq. 3).

With continuing reference to FIG. 6, the margin of gain (M_(G))determined based on the power level markers 602(1)-602(4) may be used tooptimize the DAS 500 at the cross band frequencies (f_(CB))604(1)-604(4). In a first non-limiting example, it is possible to reducepower level of the radio sources 524(1)-524(M) in FIG. 5 based on themargin of gain (M_(G)) corresponding to the cross band frequencies604(1)-604(4). In a second non-limiting example, it is possible toinclude additional components when the margin of gain (M_(G))corresponding to the cross band frequencies (f_(CB)) 604(1)-604(4)indicates that the additional components are allowable. The additionalcomponents may include additional RAUs and/or RIMs. In a thirdnon-limiting example, it is possible to modify gain range of the RAUs506(1)-506(N) in FIG. 5 based on the margin of gain (M_(G))corresponding to the cross band frequencies (f_(CB)) 604(1)-604(4).

With reference back to FIG. 5, the computing device 360 may display thegraph 600 of FIG. 6 through graphical user interfaces (GUIs). Inaddition, the computing device 360 may provide interactive GUI for anoperator/engineer to configure and/or control the signal generator 342and the receiver 346 to measure the actual loop gain (G_(LA)) anddetermine the margin of gain (M_(G)) in the DAS 500. In this regard,FIG. 7 is an exemplary interactive GUI 700 that the computing device 360of FIGS. 3 and 5 may employ to interact with an operator/engineer formeasuring the actual loop gain (G_(LA)) in the DAS 300 of FIG. 3 and theDAS 500 of FIG. 5.

With reference to FIG. 7, the interactive GUI 700 includes a usercontrol center 702 for adjusting the actual loop gain (G_(LA)) in theDAS 300 and the DAS 500. The user control center 702 includes aselection panel 704 and a settings input panel 706. The selection panel704 allows users to select a particular communications channel (e.g.,band of frequencies) for actual loop gain (G_(LA)) adjustment. Thesettings input panel 706 allows users to adjust a gain setting that isapplicable to a frequency band in the frequency spectrum of the DAS 300and the DAS 500.

FIG. 8 is a schematic diagram of an exemplary DAS 800 that can beconfigured to function as the DAS 300 of FIG. 3 and the DAS 500 of FIG.5. In this example, the DAS 800 is an optical fiber-based DAS 800. TheDAS 800 includes an optical fiber for distributing communicationsservices for multiple frequency bands. The DAS 800 in this example iscomprised of three (3) main components. One or more radio interfacesprovided in the form of radio interface modules (RIMs) 802(1)-802(M) areprovided in a central unit 804 to receive and process downlinkelectrical communications signals 806D(1)-806D(R) prior to opticalconversion into downlink optical fiber-based communications signals. Thedownlink electrical communications signals 806D(1)-806D(R) may bereceived from a base station (not shown) as an example. The RIMs802(1)-802(M) provide both downlink and uplink interfaces for signalprocessing. The notations “1-R” and “1-M” indicate that any number ofthe referenced component, 1-R and 1-M, respectively, may be provided.The central unit 804 is configured to accept the RIMs 802(1)-802(M) asmodular components that can easily be installed and removed or replacedin the central unit 804. In one example, the central unit 804 isconfigured to support up to twelve (12) RIMs 802(1)-802(12). Each RIM802(1)-802(M) can be designed to support a particular type of radiosource or range of radio sources (i.e., frequencies) to provideflexibility in configuring the central unit 804 and the DAS 800 tosupport the desired radio sources.

For example, one RIM 802 may be configured to support the PCS radioband. Another RIM 802 may be configured to support the 800 MHz radioband. In this example, by inclusion of these RIMs 802, the central unit804 could be configured to support and distribute communications signalson both PCS and LTE 700 radio bands, as an example. The RIMs 802 may beprovided in the central unit 804 that support any frequency bandsdesired, including but not limited to the US Cellular band, PCS band,AWS band, 700 MHz band, Global System for Mobile communications (GSM)900, GSM 1800, and Universal Mobile Telecommunications System (UMTS).The RIMs 802(1)-802(M) may also be provided in the central unit 804 thatsupport any wireless technologies desired, including but not limited toCode Division Multiple Access (CDMA), CDMA200, 1xRTT, Evolution-DataOnly (EV-DO), UMTS, High-speed Packet Access (HSPA), GSM, General PacketRadio Services (GPRS), Enhanced Data GSM Environment (EDGE), TimeDivision Multiple Access (TDMA), LTE, iDEN, and Cellular Digital PacketData (CDPD).

The RIMs 802(1)-802(M) may be provided in the central unit 804 thatsupport any frequencies desired, including but not limited to US FCC andIndustry Canada frequencies (824-849 MHz on uplink and 869-894 MHz ondownlink), US FCC and Industry Canada frequencies (1850-1915 MHz onuplink and 1930-1995 MHz on downlink), US FCC and Industry Canadafrequencies (1710-1755 MHz on uplink and 2110-2155 MHz on downlink), USFCC frequencies (698-716 MHz and 776-787 MHz on uplink and 728-746 MHzon downlink), EU R & TTE frequencies (880-915 MHz on uplink and 925-960MHz on downlink), EU R & TTE frequencies (1710-1785 MHz on uplink and1805-1880 MHz on downlink), EU R & TTE frequencies (1920-1980 MHz onuplink and 2110-2170 MHz on downlink), US FCC frequencies (806-824 MHzon uplink and 851-869 MHz on downlink), US FCC frequencies (896-901 MHzon uplink and 929-941 MHz on downlink), US FCC frequencies (793-805 MHzon uplink and 763-775 MHz on downlink), and US FCC frequencies(2495-2690 MHz on uplink and downlink).

With continuing reference to FIG. 8, the downlink electricalcommunications signals 806D(1)-806D(R) are provided to a plurality ofoptical interfaces provided in the form of optical interface modules(OIMs) 808(1)-808(N) in this embodiment to convert the downlinkelectrical communications signals 806D(1)-806D(R) into downlink opticalfiber-based communications signals 810D(1)-810D(R). The notation “1-N”indicates that any number of the referenced component 1-N may beprovided. The OIMs 808 may be configured to provide one or more opticalinterface components (OICs) that contain optical to electrical (O/E) andelectrical to optical (E/O) converters, as will be described in moredetail below. The OIMs 808 support the radio bands that can be providedby the RIMs 802, including the examples previously described above.

The OIMs 808(1)-808(N) each include E/O converters to convert thedownlink electrical communications signals 806D(1)-806D(R) into thedownlink optical fiber-based communications signals 810D(1)-810D(R). Thedownlink optical fiber-based communications signals 810D(1)-810D(R) arecommunicated over a downlink optical fiber-based communications medium812D to a plurality of RAUs 814(1)-814(S). The notation “1-S” indicatesthat any number of the referenced component 1-S may be provided. 0/Econverters provided in the RAUs 814(1)-814(S) convert the downlinkoptical fiber-based communications signals 810D(1)-810D(R) back into thedownlink electrical communications signals 806D(1)-806D(R), which areprovided to antennas 816(1)-816(S) in the RAUs 814(1)-814(S) to clientdevices (not shown) in the reception range of the antennas816(1)-816(S).

E/O converters are also provided in the RAUs 814(1)-814(S) to convertuplink electrical communications signals 818U(1)-818U(S) received fromclient devices through the antennas 816(1)-816(S) into uplink opticalfiber-based communications signals 810U(1)-810U(S). The RAUs814(1)-814(S) communicate the uplink optical fiber-based communicationssignals 810U(1)-810U(S) over an uplink optical fiber-basedcommunications medium 812U to the OIMs 808(1)-808(N) in the central unit804. The OIMs 808(1)-808(N) include 0/E converters that convert thereceived uplink optical fiber-based communications signals810U(1)-810U(S) into uplink electrical communications signals820U(1)-820U(S), which are processed by the RIMs 802(1)-802(M) andprovided as uplink electrical communications signals 820U(1)-820U(S).The central unit 804 may provide the uplink electrical communicationssignals 820U(1)-820U(S) to a base station or other communicationssystem.

Note that the downlink optical fiber-based communications medium 812Dand the uplink optical fiber-based communications medium 812U connectedto each RAU 814(1)-814(S) may be a common optical fiber-basedcommunications medium, wherein for example, wave division multiplexing(WDM) may be employed to provide the downlink optical fiber-basedcommunications signals 810D(1)-810D(R) and the uplink opticalfiber-based communications signals 810U(1)-810U(S) on the same opticalfiber-based communications medium.

With continuing reference to FIG. 8, it is possible to measure theactual loop gain (G_(LA)) in the optical fiber-based DAS 800 accordingto the configurations and operations described in references of FIGS. 3and 5. In this regard, FIG. 9 is a schematic diagram of an exemplaryoptical fiber-based DAS 900 configured to enable measurement of theactual loop gain (G_(LA)). Common elements between FIGS. 3, 5, 8, and 9are shown therein with common element numbers and will not bere-described herein.

With reference to FIG. 9, in the optical fiber-based DAS 900, the RIM802(1) communicates with more than one RAU among the RAUs 814(1)-814(S).It shall be appreciated that, although only one signal loop 902 is shownbetween the RIM 802(1) and the RAU 814(1), more than one signal loop mayexist involving the RIM 802(1). The signal generator 342 is capable ofgenerating the test signal 302 in narrow band and/or broadbandfrequencies. When a narrow band frequency is generated, the narrow bandfrequency may correlate to a particular communications protocol (e.g.,LTE, WCDMA, etc.). Accordingly, the receiver 346 is configured todetermine the actual loop gain (G_(LA)) and analyze spectral data (e.g.,as a spectrum analyzer) based on the narrow band and/or broadbandfrequencies.

The DAS 300 of FIG. 3 and the DAS 500 of FIG. 5, which are configured toenable measurement of the actual loop gain (G_(LA)), may be provided inan indoor environment, as illustrated in FIG. 10. FIG. 10 is a partialschematic cut-away diagram of an exemplary building infrastructure 1000in which DASs configured to measure the actual loop gain (G_(LA)),including the DAS 300 of FIG. 3 and the DAS 500 of FIG. 5, can beemployed. The building infrastructure 1000 in this embodiment includes afirst (ground) floor 1002(1), a second floor 1002(2), and a third floor1002(3). The floors 1002(1)-1002(3) are serviced by a central unit 1004to provide antenna coverage areas 1006 in the building infrastructure1000. The central unit 1004 is communicatively coupled to a base station1008 to receive downlink communications signals 1010D from the basestation 1008. The central unit 1004 is communicatively coupled to aplurality of remote units 1012 to distribute the downlink communicationssignals 1010D to the remote units 1012 and to receive uplinkcommunications signals 1010U from the remote units 1012, as previouslydiscussed above. The downlink communications signals 1010D and theuplink communications signals 1010U communicated between the centralunit 1004 and the remote units 1012 are carried over a riser cable 1014.The riser cable 1014 may be routed through interconnect units (ICUs)1016(1)-1016(3) dedicated to each of the floors 1002(1)-1002(3) thatroute the downlink communications signals 1010D and the uplinkcommunications signals 1010U to the remote units 1012 and also providepower to the remote units 1012 via array cables 1018.

The embodiments disclosed herein include various steps. The steps of theembodiments disclosed herein may be formed by hardware components or maybe embodied in machine-executable instructions, which may be used tocause a general-purpose or special-purpose processor programmed with theinstructions to perform the steps. Alternatively, the steps may beperformed by a combination of hardware and software.

The embodiments disclosed herein may be provided as a computer programproduct, or software, that may include a machine-readable medium (orcomputer-readable medium) having stored thereon instructions, which maybe used to program a computer system (or other electronic devices) toperform a process according to the embodiments disclosed herein. Amachine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes: amachine-readable storage medium (e.g., ROM, random access memory(“RAM”), a magnetic disk storage medium, an optical storage medium,flash memory devices, etc.), and the like.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps, or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention. Since modifications, combinations,sub-combinations and variations of the disclosed embodimentsincorporating the spirit and substance of the invention may occur topersons skilled in the art, the invention should be construed to includeeverything within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A method for measuring actual loop gain in awireless distribution system, comprising: disconnecting a downlink pathinto a first contact point and a second contact point; providing atleast one test signal having a first power level from the first contactpoint to at least one remote antenna unit (RAU) on the downlink path;receiving at least one loopback test signal having a second power levelfrom the second contact point; determining a difference between thefirst power level of the at least one test signal at the first contactpoint and the second power level of the at least one loopback testsignal at the second contact point; determining an actual loop gain ofthe wireless distribution system based on the determined differencebetween the first power level and the second power level; and recordingthe actual loop gain of the wireless distribution system in at least onestorage medium.
 2. The method of claim 1, further comprising:disconnecting a head end unit (HEU) from a radio source; providing theat least one test signal corresponding to a frequency spectrum thatincludes at least one downlink frequency band having a downlink centerfrequency and at least one uplink frequency band having an uplink centerfrequency; and receiving the at least one loopback test signal in the atleast one downlink frequency band and the at least one uplink frequencyband, respectively.
 3. The method of claim 2, further comprising:identifying a cross band frequency located in the middle of the downlinkcenter frequency and the uplink center frequency; determining a crossband power level at the cross band frequency based on the second powerlevel of the at least one loopback test signal; determining a margin ofgain between the cross band power level and a predetermined threshold;and adjusting the wireless distribution system based on the margin ofgain.
 4. The method of claim 3, further comprising: modifying a gainrange of the at least one RAU based on the margin of gain correspondingto the cross band frequency; and reconnecting the HEU to the radiosource.
 5. The method of claim 2, further comprising includingadditional RAUs in the wireless distribution system when the margin ofgain corresponding to the cross band frequency indicating that theadditional RAUs are allowable.
 6. The method of claim 2, furthercomprising providing the at least one test signal that corresponds tothe at least one downlink frequency band and the at least one uplinkfrequency band located in a long-term evolution (LTE) frequency band. 7.The method of claim 1, wherein the at least one RAU comprises at leastone optical-to-electrical converter and at least oneelectrical-to-optical converter.
 8. A method for measuring actual loopgain in a wireless distribution system, comprising: disconnecting adownlink path into a first contact point and a second contact point;providing at least one test signal having a first power level from thefirst contact point to at least one remote unit on the downlink path;receiving at least one loopback test signal having a second power levelfrom the second contact point; determining a difference between thefirst power level of the at least one test signal at the first contactpoint and the second power level of the at least one loopback testsignal at the second contact point; determining an actual loop gain ofthe wireless distribution system based on the determined differencebetween the first power level and the second power level; and providingthe at least one test signal corresponding to a frequency spectrum thatincludes at least one downlink frequency band having a downlink centerfrequency and at least one uplink frequency band having an uplink centerfrequency.
 9. The method of claim 8, further comprising: disconnecting ahead end unit (HEU) from a radio source; and receiving the at least oneloopback test signal in the at least one downlink frequency band and theat least one uplink frequency band, respectively.
 10. The method ofclaim 9, further comprising: identifying a cross band frequency locatedin the middle of the downlink center frequency and the uplink centerfrequency; determining a cross band power level at the cross bandfrequency based on the second power level of the at least one loopbacktest signal; and determining a margin of gain between the cross bandpower level and a predetermined threshold.
 11. The method of claim 10,further comprising adjusting the wireless distribution system based onthe margin of gain.
 12. The method of claim 8, further comprisingproviding the at least one test signal that corresponds to the at leastone downlink frequency band and the at least one uplink frequency bandlocated in a long-term evolution (LTE) frequency band.
 13. The method ofclaim 8, further comprising providing the at least one test signal inthe at least one downlink frequency band and the at least one uplinkfrequency band located in a frequency band selected from the groupconsisting of: a six hundred six megahertz (606 MHz) band; a sevenhundred twenty-one megahertz (721 MHz) band; an eight hundred sixty-twomegahertz (862 MHz) band; and a one thousand nine hundred twentymegahertz 1920 MHz) band.
 14. The method of claim 8, wherein the atleast one RAU comprises at least one optical-to-electrical converter andat least one electrical-to-optical converter.
 15. A method for measuringactual loop gain in a wireless distribution system, comprising:disconnecting a downlink path into a first contact point and a secondcontact point; providing at least one test signal having a first powerlevel from the first contact point to at least one remote unit on thedownlink path, wherein the at least one remote unit comprises at leastone optical-to-electrical converter and at least oneelectrical-to-optical converter; receiving at least one loopback testsignal having a second power level from the second contact point;determining a difference between the first power level of the at leastone test signal at the first contact point and the second power level ofthe at least one loopback test signal at the second contact point; anddetermining an actual loop gain of the wireless distribution systembased on the determined difference between the first power level and thesecond power level.
 16. The method of claim 15, further comprising:disconnecting a head end unit (HEU) from a radio source; and providingthe at least one test signal corresponding to a frequency spectrum thatincludes at least one downlink frequency band having a downlink centerfrequency and at least one uplink frequency band having an uplink centerfrequency.
 17. The method of claim 16, further comprising providing theat least one test signal that corresponds to the at least one downlinkfrequency band and the at least one uplink frequency band located in along-term evolution (LTE) frequency band.
 18. The method of claim 16,further comprising providing the at least one test signal thatcorresponds to the at least one downlink frequency band and the at leastone uplink frequency band located in a personal communications service(PCS) frequency band.
 19. The method of claim 16, further comprisingproviding the at least one test signal that corresponds to the at leastone downlink frequency band and the at least one uplink frequency bandlocated in an advanced wireless service (AWS) frequency band.
 20. Themethod of claim 16, further comprising providing the at least one testsignal in the at least one downlink frequency band and the at least oneuplink frequency band located in a frequency band selected from thegroup consisting of: a six hundred six megahertz (606 MHz) band; a sevenhundred twenty-one megahertz (721 MHz) band; an eight hundred sixty-twomegahertz (862 MHz) band; and a one thousand nine hundred twentymegahertz 1920 MHz) band.